Semi-thermoplastic molding composition having heat-stable custom shape memory

ABSTRACT

Thermoplastic molding compositions are made from a mixture of thermoplastic material (for example, polycaprolactone), a free-radically polymerizable resin (for example, a urethane diacrylate oligomer), and free-radical initiator (for example, a visible-light cure photoinitiator). The mixture is solid at 38° C., has a melting or softening point that comfortably can be withstood by oral tissues, and can be imprinted with a heat-stable custom shape memory and semi-thermoplastic properties by shaping the composition to a desired shape and then causing or permitting the resin to undergo polymerization.

This application is a divisional application of U.S. Ser. No.08/388,156, filed Feb. 13, 1995, which is a continuation of U.S. Ser.No. 08/137,584 filed Oct. 15, 1993, now U.S. Pat. No. 5,403,188, whichin turn is a continuation of U.S. Ser. No. 07/484,695 filed Feb. 23,1990, now abandoned.

FIELD OF THE INVENTION

This invention relates to thermoplastic molding compositions. It alsorelates to dental impressiion-taking, to the manufacture of dentures,crowns, bridges and other oral prosthetic devices, and togeneral-purpose modelmaking.

BACKGROUND OF THE INVENTION

High molecular weight poly (epsilon-caprolactone) (also known as"polycaprolactone") has been used as a thermoplastic molding compoundfor general-purpose modelmaking and dentistry. References describingpolycaprolactone molding compositions include U.S. Pat. No. 4,835,203,Kokai (Japanese Published Pat. Appl.) Nos. 63-171554 and 63-270759, andTONE® POLYMERS P-300 AND P-700 High Molecular Weight CaprolactonePolymers (1988 product literature of Union Carbide Corp.). Thepolycaprolactone described in Kokai No. 63-171554 is said to bepolymerized in the presence of a small amount of epoxy resin, which issaid to improve the hydrolysis resistance of the polycaprolactone.

Deldent Dental Supplies Co., Ltd. sells a heat-softenable custom traymaterial referred to as the "formable base impression" or "FBI" denturetray system. The FBI tray is immersed in hot water to soften the tray,placed in a patient's mouth while warm and shaped to conform to thepatient's arch. The FBI tray is said to return to its originalconfiguration if immersed again in hot water.

U.S. Pat. Nos. 4,240,415 and 4,483,333 describe radiation-crosslinkedpolycaprolactone orthopedic casts. The patents refer to the possibleinclusion of "chemicals containing two or more double bonds in eachmolecule". The casts are radiation-crosslinked using several 5 megaradexposures in an electron beam apparatus.

SUMMARY OF THE INVENTION

The above-described thermoplastic molding compositions lack heat-stablecustom shape memory. In other words, when the compositions are heated,formed into a desired or "custom" shape, then cooled, the resultingmodel does not have a permanent memory for the custom shape. Whenreheated, the warmed model may undergo creep and distortion, or evenmelt completely. When the FBI tray is reheated, it is said to return toits original (non-custom) shape. Accordingly, heat can cause the desiredcustom shape to be obliterated or undesirably distorted.

We believe that no previous commercially-available thermoplastic dentalmolding compositions have provided heat-stable custom shape memory (forbrevity, "hot custom memory"). The molding compositions of our inventionhave hot custom memory, and it is manifested by a semi-permanent shapememory that can be deliberately imparted to (or imprinted on) thecomposition by the user. The memory has heat resistance that overcomesthe normal thermoplastic behavior of the composition before the memoryis imprinted. Accordingly, the compositions can be said to besemi-thermoplastic rather than thermoplastic.

The present invention provides a molding composition useful for dentalimpressioning and general-purpose modelmaking, comprising a homogeneousblend of a thermoplastic material (for example, polycaprolactone), afree-radically polymerizable resin (for example, a urethane diacrylateoligomer), and a free-radical initiator (for example, a visible-lightphotoinitiator), the blend being solid at 38° C. and having a melting orsoftening point that comfortably can be withstood by oral tissues, thecomposition having semi-thermoplasticity and hot custom memory after theresin is polymerized.

The invention also provides a method for making an impression of dentaltissue, comprising the steps of a) enveloping the tissue with a moltenor softened molding composition comprising the above mentionedhomogeneous blend, and, in either order, b) cooling the composition sothat it solidifies and c) causing or permitting the free-radicallypolymerizable resin to undergo polymerization, whereby asemi-thermoplastic dental tissue impression having hot custom memory isobtained.

The molding compositions of the invention have improved physicalproperties in both the warm and cool states, especially when acustom-molded shape prepared from a composition of the invention isaccidentally or intentionally subjected to elevated temperatures.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 is a plot of viscosity vs. percent acrylate resin for thecompositions of Runs 1-11 of EXAMPLE 1;

FIG. 2 is a plot of storage modulus vs. percent acrylate resin for thecompositions of Runs 1, 6, 7, 10 and 11 of EXAMPLE 1; and

FIG. 3 is a plot of storage modulus for the compositions of Runs 1 and 2of EXAMPLE 1, showing the effect of imparting hot custom memory to thecomposition of Run 2 under various conditions.

DETAILED DESCRIPTION

A variety of thermoplastic materials can be used in the moldingcompositions of the invention. Selection of the thermoplastic materialshould be based in part on the desired end use for the moldingcomposition and the desired properties of the composition in the moltenor softened ("warm") and solid ("cool") states. The warm state ischaracterized by appreciable mass flow of the molding composition undermoderate (hand) pressure at some temperature between body temperature(about 38° C.) and the maximum temperature that comfortably can bewithstood by oral tissues. This maximum temperature is generally thoughtto be about 75° C., although a maximum of about 65° C. is preferred. Thecool state is characterized by sufficient strength and stiffness topermit an acceptably accurate dental impression to be made from themolding composition, and by minimal apparent mass flow of the moldingcomposition under moderate pressure at temperatures below 38° C.

The warm and cool state properties permit the molding composition to beheated to a moderate temperature, manually shaped in the mouth whilewarm to conform to the shape of hard and soft oral tissue, and cooledwithin the mouth to form a substantially rigid model.

Representative thermoplastic materials include polyesters andpolyurethanes such as those described in U.S. Pat. Nos. 3,382,202,4,059,715, 4,182,829, 4,327,013, 4,361,538, 4,552,906 and 4,569,342, andcopolymers such as those described in U.S. Pat. Nos. 4,659,786,4,740,245 and 4,768,951. The thermoplastic material preferably is ahomopolymer or copolymer of epsilon-caprolactone. The polycaprolactoneoptionally can contain property-modifying or cross-linkable functionalgroups (for example hydroxyl, acrylate, methacrylate, epoxy, isocyanatoor vinyl groups) if desired.

Preferred polycaprolactones have the formula: ##STR1## where R¹ is anaromatic or a straight chain or branched aliphatic backbone, which canoptionally contain one or more non-interfering substituents such ashydroxyl or amine groups, w is 1 if R¹ is hydrogen, and w otherwise hasan average value of about 1 to about 4, M is oxygen or --NR² -- where R²is hydrogen or a non-interfering aromatic or aliphatic group, and theproduct of w times x is greater than about 35.

Blends of polycaprolactones can also be employed. Suitablepolycaprolactone blends are described in our copending applicationSerial No. (Attorney's Docket No. 44686 U.S.A. 1A), the disclosure ofwhich is incorporated in this specification by reference.

Preferred commercially available polycaprolactone polymers include "TONEP-700" and "TONE P-767" (40,000 molecular weight) and "TONE P-300"(10,000 molecular weight) polycaprolactone from Union Carbide Corp., andthe "CAPA" polycaprolactones "630" (30,000 molecular weight), "640"(40,000 molecular weight), "650" (50,000 molecular weight), and "656"(56,000 molecular weight ) from Interox.

The free-radically polymerizable resin contains at least oneethylenically unsaturated monomer, oligomer, or polymer capable ofundergoing addition polymerization. Suitable monomers include mono-, di-or polyfunctional acrylates and methacrylates such as methyl acrylate,methyl methacrylate, ethyl acrylate, isopropyl methacrylate, n-hexylacrylate, styryl acrylate, allyl acrylate, glycerol diacrylate, glyceroltriacrylate, ethyleneglycol diacrylate, diethyleneglycol diacrylate,triethyleneglycol dimethacrylate, 1,3-propanediol diacrylate,1,3-propanediol dimethacrylate, trimethylolpropane triacrylate,1,2,3-butanetriol trimethacrylate, 1,4-cyclohexanediol diacrylate,pentaerythritol triacrylate, pentaerythritol tetraacrylate,pentaerythritol tetramethacrylate, sorbitol hexacrylate,bis[1-(2-acryloxy)]-p-ethoxyphenyldimethylmethane,bis[1-(3-acryloxy-2-hydroxy)]-p-propoxyphenyldimethylmethane,tris-hydroxyethylisocyanurate triacrylate, beta-methacryl aminoethylmethacrylate, and mixtures thereof. Other suitable monomers includeunsaturated amides such as methylene bis-acrylamide, methylenehis-methacrylamide, 1,6-hexamethylene bis-acrylamide anddiethylenetriamine tris-acrylamide. Suitable oligomeric or polymericresins include 200 to 500 molecular weight polyalkylene glycols,acrylated or methacrylated oligomers such as those of U.S. Pat. No.4,642,126, acrylated urethanes such as "SARTOMER" 9503, 9504 and 9505(Sartomer Corp.), "INTEREZ" CMD 8803, 8804 and 8805 (Radcurespecialties, Inc.), and "PHOTOMER" 6060, 6110 and 6160 (Henkel Corp.),as well as acrylated polyester oligomers such as "EBERCRYL" 830 (RadcureSpecialties, Inc.). Mixtures of free-radically polymerizable monomers,oligomers or polymers can be used if desired.

The free-radically polymerizable resin can if desired be cured using aconventional chemical initiator system, such as a combination of aperoxide and an amine. However, chemical cure initiator systemstypically require at least partial ingredient separation before use. Theresin is preferably cured using a photoinitiator, optionally combinedwith a suitable photosensitizer or accelerator. The photoinitiatorshould be capable of generating free radicals for additionpolymerization at some wavelength between 200 and 800 nm. Suitablephotoinitiators include alpha-diketones, monoketals of alpha-diketonesor ketoaldehydes, acyloins and their corresponding ethers,chromophore-substituted halomethyl-s-triazines, chromophore-substitutedhalomethyl-oxadiazoles, aryliodonium salts, and other commerciallyavailable ultraviolet ("UV") and visible light photoinitiators.Preferred photoinitiator systems include a mono or diketonephotoinitiator together with a suitable donor compound or accelerator,such as the systems described in U.S. Pat. Nos. 3,427,161, 3,756,827,3,759,807, 4,071,424, 4,828,583, U.K. Pat. Specification No. 1,304,112,European Published Pat. Appl. No. 150,952 and Chem. Abs. 95:22570 4U.

The molding compositions of the invention can contain a wide variety ofadjuvants depending upon the desired end use. Suitable adjuvants includesolvents, diluents, plasticizers, pigments, dyes, inorganic or organicfibrous or particulate reinforcing or extending fillers, thixotropicagents, indicators, inhibitors, stabilizers, UV absorbers, medicaments(e.g., leachable fluorides), biocides and the like. For custom trayapplications, the molding composition preferably contains one or morefillers that limit the composition's 60° C. relaxation stress atequilibrium, as described in our copending application Serial No.(Attorney's Docket No. 45066 U.S.A. 3A), the disclosure of which isincorporated in this specification by reference.

The types and amounts of ingredients in the molding compositions of theinvention usually will be empirically selected. The thermoplasticmaterial and free-radically polymerizable resin preferably are presentin "major proportion" and "minor proportion", respectively. By this wemean that the composition preferably contains a higher weight percent ofthermoplastic material than of polymerizable resin.

The composition should remain substantially homogeneous (that is, itshould not undergo macroscopic phase separation or fillersedimentation). Subject to the effects of any imprinted hot custommemory, the composition preferably should retain its desired physicalproperties even if repeatedly cycled between the warm and cool states.Thus the selection of ingredients can be guided in part by the desire topreserve homogeneity and thermal reversibility. Also, the amount ofpolymerizable resin and initiator should be sufficient to provide thedesired degree of hot custom memory. Lower amounts of resin tend toincrease susceptibility to creep after the custom memory has beenimparted to the composition. Higher resin amounts tend to decreaseelasticity.

As a further guide, the preferred amounts of thermoplastic material,polymerizable resin, initiator and filler for dental impressioning areas follows:

    ______________________________________                                        Ingredient       Preferred Weight %                                           ______________________________________                                        Thermoplastic material                                                                         up to 90                                                     Polymerizable resin                                                                            up to 50                                                     Initiator        up to 10                                                     Filler            0-70                                                        ______________________________________                                    

The ingredients in the molding composition can be blended by hand or bymechanical mixing. The ingredients preferably are warmed sufficiently tomelt the thermoplastic material, but if desired can be mixed at lowertemperatures. Any suitable mixing device can be used, including kettlesequipped with a mechanical stirrer, extruders, rubber mills, and thelike.

The molding composition can be put up in a variety of forms includingpreformed sheets, arch-shaped trays, ropes, buttons, woven or non-wovenwebs and the like. The composition can be shaped in a variety of waysincluding extrusion, injection molding and web processing using acoating knife or rollers. The composition can be sold unwrapped, looselywrapped in a package, or packaged in tubes, syringes, flexible outerplastic skins, plastic or metal trays and the like. The composition canbe extruded or cast in mono-, bi-, or poly-layers (for example, aplanarlayers or layers arranged in core-shell fashion) in which each layer hasa selected melting temperature, viscosity, modulus, stickiness, or otherdesired physical properties.

The molding composition can be converted from the cool state to the warmstate by using a variety of energy sources. The composition can beimmersed in a heated bath containing a suitable inert liquid (forexample, water or a fluorochemical fluid) that will not dissolve orswell the composition in either its cool or warm states. The compositioncan also be softened using heat sources such as a hot air gun, hotplate, conventional oven, infrared heater or microwave oven. Thecomposition can be encased in a plastic pouch, syringe or othercontainer which is in turn heated (e.g. electrically), or subjected toone or more of the above-mentioned heating methods.

Transforming the molding composition from a warm state to a cool staterequires loss of thermal energy and can be carried out using a varietyof cooling techniques. Cooling can take place under ambient conditionsin the presence of air only. Cooling can be expedited using forced air,cold water, ice, or heat sinks such as chilled "cold packs" or flexiblepouches containing low boiling inert liquids. Of particular interest forboth dental and orthopedic applications are chilled cold packs inflexible pouches that have been preshaped to match the contours of themodel being cooled. For example, flexible pouches containing a chilledcoolant can be fabricated in the shape of a full arch or quadrant andplaced intraorally in contact with the warm molding composition.Analogously, a large coolant-filled blanket can be draped around anorthopedic casting or splint material prepared from a moldingcomposition of the invention.

Hot custom memory is imparted to the molding composition by allowing orcausing the free-radically polymerizable resin and initiator to harden(for example, by exposing a composition containing a photoinitiator to asuitable light source). Polymerization can take place before or afterthe warmed, softened model is allowed to cool, although carrying outpolymerization after cooling will tend to lengthen polymerization times.After polymerization, the model preferably retains sufficient elasticityto permit it to be removed from undercut surfaces such as the undercutstypically found in the oral cavity.

The polymerized, cooled model will exhibit hot custom memory.Accordingly, it will be more resistant to heat and handling stressesthan models made from the thermoplastic material alone. If the model isaccidentally distorted, it can be returned to its custom shape byreheating it in a relaxed condition. For example, the model can beimmersed in a hot water bath and removed for cooling after the customshape has reappeared. While still in the warm state, it will remainpliable, and accordingly will exhibit semi-thermoplasticity. Thispermits the custom shape to be adjusted if desired.

A simplified dental impression system can be prepared from the moldingcomposition. Traditional impressioning systems employ one or more lowviscosity, flowable elastomeric materials such as an alginate,hydrocolloid, polyvinylsiloxane, polyether, or polysulfide contained ina fairly rigid adhesive-coated plastic or metal arch-shaped tray. Theelastomeric material often is applied both to the dental tissue to bemodeled and to the tray. The elastomeric material and surrounding trayare subsequently pressed against the dental tissue, and left in placeuntil the elastomeric material has hardened. This traditional processinvolves several materials and steps, material waste and fairly lengthyset times.

The present invention permits impressioning using a monolayer or abilayer thermoplastic molding composition. The monolayer model, or atleast one layer of the bilayer model, is made from a molding compositionof the invention. In a preferred embodiment, a flat sheet or a preformedarch-shaped tray is made from two coextruded thermoplastic layers. Thephysical properties of each layer emulate in part the properties of aconventional rigid tray and the elastomeric material respectively. At asuitable elevated temperature the "tray" layer becomes a conformable,non-sticky melt (thereby permitting the warm tray layer to behand-shaped into a custom tray configuration) and the "elastomer" layerexhibits good flow and low viscosity (thereby permitting the warmelastomer layer to flow around tooth structure and provide an accuratemodel). The warm bilayer construction provides easy placement, accurateimpressioning, and efficient use of materials. Cooling can take placerapidly, and in less time than is required to harden a conventionalimpression. Once cooled, the tray layer exhibits sufficient rigidity todiscourage distortion of the impression during removal from the mouth orduring subsequent handling. If the tray layer is made from a moldingcomposition of the invention and is polymerized after the desired customshape has been attained, then the hot custom memory properties of thetray layer discourage creep and distortion. The elastomer layer providesstable, accurate modeling of hard and soft dental tissue. If theelastomer layer is made from a molding composition of the invention,then the hot custom memory properties of the elastomer layer aid inmaking accurate casts using heated gypsum stone substitutes such ashot-melt thermoplastics. In either embodiment, the model can be shippedthrough the mail and exposed to elevated temperatures with reduced riskthat the model will melt or otherwise become permanently distorted.

If desired, a custom impression tray can be formed from a moldingcomposition of the invention and filled with a conventional elastomericimpression material (for example, a silicone elastomer). By shaping thetray in the mouth before (or if desired, after) it is filled withelastomer, the tray volume and required amount of elastomer will beminimized.

The molding compositions of the invention have many other uses. Forexample, they can be used to prepare crowns, bridges, dentures, splintsand pontics. They can also be used to prepare shapeable orthopedic castsand splints. They can be used in modelmaking, for example in tool anddie-making. They will find general use in applications requiring rapid,accurate shaped object formation.

The following examples are offered to aid in understanding the inventionand are not to be construed as limiting its scope. Unless otherwiseindicated, all parts and percentages are by weight.

EXAMPLE 1

70 Parts "TONE P-767" (40,000 molecular weight) polycaprolactone and 30parts "SR-9503" urethane diacrylate oligomer were placed in an openvessel and heated in an oven at 80° C. until both components were fluid.The vessel was transferred to an 80° C. water bath and the mixturestirred until homogeneous. While working under a safelight, 0.50 partscamphorquinone ("CPQ") and 0.50 parts p-ethyldimethylaminobenzoate("EDMAB") were dissolved in the mixture with stirring. The resultantblend was poured onto polyester sheeting atop a horizontal platform. Asecond polyester sheet was placed atop the molten mass. A roller wasused to form the blend into sheets of approximately 2-4 mm thickness.The sheets were transparent while warm and became opaque when cooledunder a stream of cold water.

Using a similar procedure a control composition (containing 100%polycaprolactone) and fifteen additional polycaprolactone/acrylateblends were prepared. Set out below in TABLE I are the types and amountsof polycaprolactone ("PCL") and acrylate in each composition, andseveral physical properties for each composition. Warm state viscositywas measured at 65° C. using a rheometric dynamic analyzer (Rheometrics,Inc.) operated at 20% maximum strain and 1 radian/second strain rate.

Cool state storage modulus was measured at 30° C. on the rheometricdynamic analyzer, operated at 1.4% maximum strain and a 10 radian/secondstrain rate, on samples subjected to several curing conditions. Thesamples were 1) not irradiated 2) irradiated under "cold" conditionswhile the sample was at 25° C. in a custom-molded configuration, using a"VISILUX 2" dental curing lamp (3M) operated for two minutes, or 3)irradiated under "hot" conditions while the sample was at about 50°-55°C. in a custom-molded configuration, using the same lamp and time as in2). These three conditions are identified as "NIR", "IR Cold", and "IRHot" in the tables that follow

Dimensional stability was evaluated using a modified version of AmericanDental Association (ADA) Test Specification No. 19 (J.A.D.A., 94, 733(1977)). Each molding composition was heated to 80° C. until molten andpoured onto the ruled die prescribed in the Test Specification. Atransparent rigid plate was placed atop the molten composition, andsecured to the ruled die with a clamp. Selected samples of thecomposition were left unitradiated or irradiated while hot. The moltencomposition was allowed to cool for 5 minutes at room temperature.Selected molding composition samples were irradiated while cold. Theclamp and solidified molding composition were removed from the die. Theresulting model was stored at 23°±1° C. and 50±5% relative humidity for24 hours. Dimensional stability was determined by comparing thedistances between the ruled lines on the model and on the ruled dieusing an optical comparator.

                                      TABLE I                                     __________________________________________________________________________                                        Dimensional                                                        Modulus, 30° C.                                                                   stability,                                                    Viscosity                                                                          dyne/cm.sup.2 × 10.sup.8                                                           % shrinkage                               Run                                                                              PCL    Acrylate  65° C.,                                                                         IR  IR     IR IR                                 no.                                                                              Type                                                                              Parts                                                                            Type   Parts                                                                            kilopoise                                                                          NIR.sup.2                                                                         Cold.sup.3                                                                        Hot.sup.4                                                                        NIR Cold                                                                             Hot                                __________________________________________________________________________    1  P-767.sup.1                                                                       100                                                                              None    0 85.0 11.7                                                                              .sup. NM.sup.5                                                                    NM 0.70                                                                              NM NM                                 2  "   70 SR-9503.sup.6                                                                        30 52.7 4.2 7.8 5.5                                                                              0.47                                                                              0.49                                                                             0.55                               3  "   55 "      45 9.2  0.9 5.2 5.6                                                                              .sup. NV.sup.7                                                                    0.40                                                                             0.45                               4  "   70 SR-9504.sup.8                                                                        30 35.1 5.9 4.9 4.5                                                                              0.54                                                                              0.58                                                                             0.53                               5  "   55 "      45 12.8 3.3 4.3 8.3                                                                              0.57                                                                              0.57                                                                             0.51                               6  "   70 SR-9505.sup.9                                                                        30 35.0 6.1 11.0                                                                              9.2                                                                              0.58                                                                              0.56                                                                             0.49                               7  "   55 "      45 20.4 3.8 10.0                                                                              13.9                                                                             NV  0.28                                                                             0.41                               8  "   70 CMD-8803.sup.10                                                                      30 32.8 0.01                                                                              6.2 9.7                                                                              0.51                                                                              0.35                                                                             0.46                               9  "   55 "      45 6.2  0.8 6.4 4.8                                                                              NM  0.34                                                                             0.41                               10 "   70 CMD-8805.sup.11                                                                      30 23.6 9.1 24.1                                                                              16.9                                                                             0.57                                                                              0.69                                                                             0.70                               11 "   55 "      45 11.3 3.8 0.2 31.3                                                                             0.38                                                                              0.66                                                                             0.73                               12 "   70  230.sup.12                                                                          30 11.4 7.6 8.2 7.3                                                                              NV  0.41                                                                             0.50                               13 "   55 "      45 15.4 5.6 5.7 6.7                                                                              NV  0.25                                                                             0.44                               14 "   70 4287.sup.13                                                                          30 12.7 6.1 9.2 8.6                                                                              0.43                                                                              0.59                                                                             0.58                               15 "   55 "      45 4.9  4.1 6.3 4.5                                                                              0.39                                                                              0.53                                                                             0.49                               16 "   70  830.sup.14                                                                          30 0.1  0.03                                                                              19.0                                                                              11.6                                                                             0.32                                                                              0.83                                                                             0.63                               17 "   55 "      45 0.03 NM  12.7                                                                              5.5                                                                              0.23                                                                              1.01                                                                             1.16                               __________________________________________________________________________     .sup.1 "TONE P767" 40,000 molecular weight polycaprolactone (Union Carbid     Corp.).                                                                       .sup.2 "NIR"--Not irradiated.                                                 .sup.3 "IR" Cold" = Irradiated cold.                                          .sup.4 "IR Hot" = Irradiated hot.                                             .sup.5 "NM" = Not measured.                                                   .sup.6 "SR9503" urethane diacrylate oligomer (Sartomer Corp.).                .sup.7 "NV" = Measurement attempted but not recorded due to poor die          reproduction.                                                                 .sup.8 "SR9504" urethane diacrylate oligomer (Sartomer Corp.).                .sup.9 "SR9505" urethane diacrylate oligomer (Sartomer Corp.).                .sup.10 "CMD8803" urethane diacrylate oligomer (Radcure Specialties,          Inc.).                                                                        .sup.11 "CMD8805" urethane diacrylate oligomer (Radcure Specialties,          Inc.).                                                                        .sup.12 "Ebercryl 230" Urethane acrylate (Radcure Specialties, Inc.).         .sup.13 "Ebercryl 4287" Aromatic urethane acrylate (Radcure Specialties,      Inc.).                                                                        .sup.14 "Ebercryl 830" polyester hexacrylate (Radcure Specialties, Inc.).

The above data illustrates the extent to which a reduction in warm stateviscosity, an increase in cool state modulus, and a reduction inshrinkage can be attained by blending polycaprolactone withfree-radically polymerizable resin and photoinitiator, and irradiatingthe blend under hot or cold conditions. The data is further illustratedin FIGS. 1 and 2. FIG. 1 shows an unsmoothed plot of viscosity at 65° C.vs. percent polymerizable resin for Runs 1-11 of TABLE I. Curves Athrough E connect the data points for blends containing thepolymerizable resins "SR-9503", "SR-9504", "SR-9505", "CMD-8803" and"CMD-8805", respectively.

FIG. 2 shows an unsmoothed plot of storage modulus at 30° C. vs. percentpolymerizable resin for the compositions of Runs 1, 6, 7, 10 and 11.Curves F, G, and H are for compositions containing "SR-9505"polymerizable resin (Runs 6 and 7) in the unirradiated, irradiated coldand irradiated hot conditions, respectively. Curves I, J and K are forcompositions containing "CMD-8805" polymerizable resin (Runs 10 and 11)in the unitradiated, irradiated cold and irradiated hot conditions,respectively. As shown by the curves, the irradiated compositionsexhibited improved modulus compared to unirradiated compositions.

Referring now to FIG. 3, an unsmoothed plot of storage modulus vs.temperature is shown for Run 1 (curve L) and Run 2 (curves M, N and O)of TABLE I. The measurements were made using a rheometric dynamicanalyzer operated at 1.4% maximum strain and a 10 radians/second strainrate. Curve L is a control, and illustrates the substantial decrease inmodulus that occurs when the temperature of the molding compositionexceeds its melting or softening temperature. Curves M through Oillustrate the modulus of a polycapro-lactone/polymerizable resin blendin the unirradiated, irradiated cold and irradiated hot conditions,respectively. As shown by curves N and O, modulus remains high and isrelatively unaffected by temperature. These compositions thus havesignificantly improved heat resistance.

EXAMPLE 2

20 Parts "IMSIL A-25" ground quartz filler (Illinois Minerals) wereadded with stirring to an open vessel containing 24.5 parts "CMD-8805"urethane acrylate oligomer, 0.5 parts CPQ and 1.0 parts EDMAB. Themixture was stirred at 80° C. until homogeneous. 54 Parts "TONE P-767"polycaprolactone were added to the vessel, and the mixture was heatedwith stirring at 80° C. until molten.

Using a similar procedure, a control composition containing no fillerand eight additional compositions containing various types and amountsof fillers were prepared. Set out below in TABLE II are the amounts ofpolycaprolactone ("PCL") and polymerizable resin ("Resin") in eachcomposition, the type and amount of filler in each composition, and themodulus for compositions that were not irradiated ("NIR") or irradiatedwhile cold ("IR Cold").

                                      TABLE II                                    __________________________________________________________________________    Ingredients                   Modulus, 30° C.,                         Run PCL  Resin Filler         dyne/cm.sup.2 × 10.sup.8                  no. Amount                                                                             Amount                                                                              Type     Amount                                                                              NIR IR cold                                     __________________________________________________________________________    1   74.0 24.5   --      --    3.2 8.1                                         2   54.0 24.5  "IMSIL".sup.1                                                                          20    5.1 7.1                                         3   39.0 19.5    "      40    .sup. NM.sup.2                                                                    2.8                                         4   54.0 24.5  "VICRON".sup.3                                                                         20    1.5 8.6                                         5   39.0 19.5    "      40    NM  9.1                                         6   54.0 24.5  "DUROSIL".sup.4                                                                        20    7.0 8.1                                         7   54.0 24.5  "OX-50".sup.5                                                                          20    6.8 6.7                                         8   54.0 24.5  Treated "OX-50".sup.6                                                                  20    3.9 9.4                                         9   54.0 24.5  Quartz.sup.7                                                                           20    8.4 6.9                                         __________________________________________________________________________     .sup.1 "IMSIL A25" Quartz filler (Illinois Minerals).                         .sup.2 NM = not measured                                                      .sup.3 "VICRON" calcium carbonate (Pfizer Corp.).                             .sup.4 "DUROSIL" silica (North American Silica Co.).                          .sup.5 "OX50" pyrogenic silica (Degussa).                                     .sup.6 OX50" pyrogenic silica treated with gammamethacryloxypropyl            trimethoxysilane.                                                             .sup.7 quartz treated with gammamethacryloxypropyl trimethoxysilane.     

EXAMPLE 3

An aliphatic segmented thermoplastic polyester was prepared by measuringout the ingredients set out below in TABLE III:

                  TABLE III                                                       ______________________________________                                        Ingredient            Parts                                                   ______________________________________                                        Poly(tetramethylene ether) diol.sup.1                                                               49.53                                                   Adipic acid           29.21                                                   1,6-hexanediol        21.26                                                   Antioxidant.sup.2      0.10                                                   Antimony oxide         0.10                                                   ______________________________________                                         .sup.1 "POLYMEG 2000" (Quaker Oats Chemical).                                 .sup.2 "IRGANOX 1010" (Ciba Geigy Corp.).                                

The "POLYMEG 2000" diol and 1,6-hexanediol were transferred to a threeneck flask fitted with a mechanical stirrer, condenser, "Dean-Stark"trap, heating mantle, thermometer and nitrogen inlet. The diols werestirred at moderate speed under a nitrogen purge for 5-10 minutes whileheating to a temperature of 100° C. Adipic acid was slowly added and themixture heated to a temperature of about 140°-150° C. Water begancollecting in the trap. The reaction was continued until at least 80%complete on the basis of water volume collected. The reaction mixturewas cooled to 150° C. and the trap removed. The antioxidant and antimonyoxide were then added to the flask. The flask was purged with nitrogenfor 5 minutes. Following the purge, the flask was attached to a vacuumline and the pressure reduced while maintaining a reaction temperatureof 150° C. After 30 to 60 minutes a vacuum of <0.1 mm Hg was attainedand the reaction temperature increased to 230° C. The reaction wascontinued until the acid number had decreased to less than <1 mg KOH gmsample. The resulting semi-crystalline thermoplastic compositioncontained about 53% amorphous segment content and exhibited rubbery,elastomeric properties in the solid state.

A blend of this segmented polyester and a free-radically polymerizableacrylate resin ("CMD-8803", Interez) was prepared by transferring theingredients set out below in TABLE IV to a glass vessel heated to 80°C.:

                  TABLE IV                                                        ______________________________________                                        Ingredient         Parts                                                      ______________________________________                                        Segmented polyester                                                                              80.0                                                       Urethane acrylate  20.0                                                       CPQ                0.25                                                       EDMAB              0.50                                                       ______________________________________                                    

The ingredients were heated until molten and mixed thoroughly with aspatula until homogeneous. The resultant blend was cast into a sheet andcooled, yielding a thermoplastic elastomer.

The neat segmented polyester and the segmented polyester/acrylate blendwere evaluated by measuring viscosity, modulus, and shrinkage asdescribed above. In addition, compression set was evaluated using amodified version of ADA Test Specification No. 19. Each composition washeated to 80° C. until molten and transferred to the standardcompression set cylindrical mold prescribed in the Test Specification.The mold endplates were clamped into place and the mold and its contentscooled in a 22° C. water bath for 5 minutes. The resulting solidifiedmodel was removed from the mold. Each model was axially compressed 1.0mm for 30 seconds using a metered screw clamp. The clamp was releasedand a measurement of permanent deformation recorded one minute later.The percentage change in cylinder height was calculated to determinecompression set.

Strain-in-compression was evaluated using a modified version of ADA TestSpecification No. 19. Cylindrical models were prepared according to thecompression set test described above. The cylinder height was measured,a 1.125 kg mass was placed atop the cylinder, and a second heightmeasurement was recorded thirty seconds later. The percentage change incylinder height was calculated to determine strain-in-compression.

The results for each composition are set out below in TABLE V:

                                      TABLE V                                     __________________________________________________________________________                  Modulus,                                                                              Dimensional                                                           30° C.,                                                                        stability,                                              Polyester/                                                                             Viscosity,                                                                         dyne/cm.sup.2 × 10.sup.8                                                        % shrinkage                                             Run                                                                              acrylate                                                                            65° C.,                                                                         IR     IR  Compression                                                                          Strain-in-                                no.                                                                              ratio kilopoise                                                                          NIR.sup.1                                                                         Hot.sup.2                                                                         NIR                                                                              Hot set, % compression, %                            __________________________________________________________________________    1  100/0 2.7  0.5 NM.sup.3                                                                          0.25                                                                             NM  0.96   0.63                                      2  80/20 2.2  0.6 0.8 0.23                                                                             0.12                                                                              0.84   1.78                                      __________________________________________________________________________     .sup.1 "NIR" = Not irradiated.                                                .sup.2 "IR Hot" = Irradiated hot.                                             .sup.3 "NM" = Not measured.                                              

EXAMPLE 4

Three compression set cylinders were prepared from thepolycaprolactone/acrylate blend of Run 7 of TABLE I, and evaluated forcompression set as in EXAMPLE 3. However, one cylinder was irradiatedwith a "VISILUX 2" curing light through the clamped clear plasticendplates while the composition was in the molten state. The secondcylinder was irradiated after the composition had been cooled andremoved from the cylindrical mold. The third cylinder was notirradiated. The three cylinders were each removed from the mold andevaluated for hot custom memory in the following manner. Each cylinderwas independently placed in an 80° C. water bath for 5 minutes. Theunitradiated cylinder melted and failed to maintain its cylindricalshape. Both of the irradiated cylinders exhibited only softening to anelastomeric condition. Each of the irradiated cylinders was measuredlengthwise, axially compressed 2.4 mm and cooled while compressed sothat a semi-permanent 2.4 mm lengthwise distortion was imparted. Thecylinders were then reheated in an 80° C. water bath for 5 minutes,allowed to cool until solid and then measured lengthwise for comparisonto the original cylinder length prior to compression. The cylinderirradiated in the solid state exhibited 99.86% recovery, and thecylinder irradiated in the molten state exhibited 99.75% recovery. Theseirradiated samples thus exhibited excellent hot custom memory, whereasthe unitradiated cylinder exhibited no memory.

EXAMPLE 5

Inlay accuracy was evaluated by heating the molding compositions of Runs8-11 of TABLE I and Runs 1 and 2 of TABLE V to 65° C., and using theresulting molten compositions to make an impression of a class II MODpreparation on the lower left first molar of a "TYPODONT" model(Columbia Dentoform Corp.). The molten compositions were applied evenlyto the second premolar, the prepared first molar and the second molar,and pressed into place using finger pressure while in the transparent,molten state. Each composition was cooled for 60 seconds using a streamof cold water and then removed from the TYPODONT model yielding acompleted opaque impression. A standard gypsum "stone" model was pouredin each impression. The hardened stone model was easily removed from theimpression by slightly warming the impression to about 60° C. in a waterbath. An inlay was fabricated on each stone model in the followingmanner. A thin film of room-temperature vulcanizing silicone ("IMPRINT",3M) was applied to the MOD preparation on the stone model and allowed tocure. Light curable restorative material ("SILUX PLUS", 3M) was tampedinto the MOD preparation and shaped and carved to provide proper fit andanatomy. The restorative material was irradiated with a VISILUX 2 curinglamp for 60 seconds. The resulting photo-hardened inlays were removedfrom the stone model and evaluated for overall fit on the originalTYPODONT model preparation. Inlays were rated by two evaluators asproviding excellent ("++"), acceptable ("+"), or unacceptable ("-") fit.The results are set out below in TABLE VI:

                  TABLE VI                                                        ______________________________________                                               Thermo-                                                                       plastic/                                                                             Inlay fit                                                       Table Run    acrylate       IR    IR     IR                                   no.   no.    ratio    NIR.sup.1                                                                           Hot.sup.2                                                                           Cold-IO.sup.3                                                                        Cold-EO.sup.4                        ______________________________________                                        I     8      70/30    ++    ++    +/++   +/-                                  I     9      55/45    -     -     ++     ++                                   I     10     70/30    -     ++    -      -                                    I     11     55/45    -     ++    ++     ++                                   V     1      100/0    ++    .sup. NM.sup.5                                                                      NM     NM                                   V     2      80/20    ++    ++    NM     NM                                   ______________________________________                                         .sup.1 "NIR" = Not irradiated.                                                .sup.2 "IR Hot" = Irradiated hot.                                             .sup.3 "IR ColdIO" = Irradiated cold "intraorally" (while on model).          .sup.4 "IR ColdEO" = Irradiated cold "extraorally" (after removal from        model).                                                                       .sup.5 "NM" = Not measured.                                              

The above data illustrates a variety of techniques for preparing inlaysfrom compositions of the invention. For some compositions, excellentinlay fit was obtained even though irradiation was not carried out untilafter the composition had been cooled to a solid state and removed fromthe model.

EXAMPLE 6

A filled thermoplastic custom tray composition was prepared by combining22.5 parts "TONE P-767" polycapro-lactone, 7.5 parts "SR-9505" urethanediacrylate, 1.2 parts "EBERCRYL 830" polyester hexacrylate, 45 parts"VICRON" calcium carbonate (Pfizer Corp.), 10 parts "SIPERNAT D-11"treated precipitated silica (North American Silica Co.), 5 parts"ULTRASIL VN-SP3" untreated precipitated silica (North American SilicaCo.), 4 parts "1156" chopped glass fibers (PPG), and 0.75 parts each CPQand EDMAB. The ingredients were stirred in a warm vessel at about 100°C. until homogeneous. The resulting mixture was cast atop polyester filminto a 2.5 mm thick sheet into which was pressed a web of "SONTARA 8000"nonwoven material (E. I. DuPont de Nemours & Co.). The warm sheet wascut into generally U-shaped pieces using a "cookie cutter" style cuttingimplement. Each piece was squeezed while still warm between two halvesof a silicone mold to form an arch-shaped, nonwoven web-linedcustomizable tray. The tray could be reheated and shaped while warm toconform to a patient's dentition. When irradiated for two minutes in a"STAR-CURE" curing chamber (Star X-ray, Inc.), a tray with hot custommemory was obtained. The tray can also be photocured by setting it undera conventional dental operatory light (for example, a "RITTER STARLIGHT", Sybron Corp.) for about two minutes per side.

EXAMPLE 7

Using the method of EXAMPLE 1, a photosettable thermoplastic compositionwas prepared by mixing the ingredients set out below in TABLE VII:

                  TABLE VII                                                       ______________________________________                                        Ingredient            Parts                                                   ______________________________________                                        "TONE P-767" Polycaprolactone                                                                       59.40                                                   "SR-9505" Urethane diacrylate                                                                       39.60                                                   CPQ                   0.50                                                    EDMAB                 0.50                                                    ______________________________________                                    

The resulting thermoplastic composition is useful as a crown and bridgematerial. A bridge was prepared in the following manner. Thethermoplastic composition was transferred to a syringe and placed in a70° C. water bath for about 5 minutes. The second molar was removed froma "TYPODONT" model, and the adjacent first and third molars wereprepared as abutment teeth. The thermoplastic composition was syringedonto the abutment teeth and into the gap between them. The compositionwas shaped while warm to form a bridge with appropriate anatomical form.The bridge was then irradiated for 30 seconds with a "VISILUX 2" curinglight. The bridge was allowed to cool, removed from the model andirradiated thoroughly for an additional 60 seconds. The bridge could befirmly reseated on the model. It could be adhered intraorally to actualabutment teeth using a standard dental adhesive such as "SCOTCHBOND"Dual Cure adhesive (3M).

EXAMPLE 8

A crown was fabricated from the composition of EXAMPLE 7. The resultingcrown was fairly rigid and could be bonded to a prepared tooth using astandard dental adhesive or cement.

EXAMPLE 9

Using the method of EXAMPLE 1, a photosettable thermoplastic custom traywas fabricated from a composition prepared by mixing together theingredients set out below in TABLE VIII:

                  TABLE VIII                                                      ______________________________________                                        Ingredient             Parts                                                  ______________________________________                                        "TONE P-767" Polycaprolactone                                                                        27.0                                                   "CMD 8805" Urethane diacrylate                                                                       12.3                                                   CPQ                    0.5                                                    EDMAB                  0.5                                                    "IMSIL A-25" Filler    10.0                                                   ______________________________________                                    

The resulting thermoplastic composition was fabricated into a partiallyformed tray having a half-moon shape and a protruding handle at themidline. The tray (excluding its handle) was suspended in a 70° C. waterbath until transparent, then shaped to fit around the full arch of a"TYPODONT" model. The tray was allowed to cool slightly and then removedfrom the model. The resulting custom tray was uniformly irradiated witha "VISILUX 2" curing light for about 2 minutes, yielding a rigidphotoset tray. The tray was placed in an 80° C. oven for 10 minutes. Itretained its shape without slumping, thus illustrating the heatresistance imparted by hot custom memory.

"EXPRESS" tray adhesive (3M) was applied to the photoset custom traywith a brush and allowed to dry for about 5 minutes. "IMPRINT" singlephase impression material (3M) was syringed onto the model and into thetray. The tray was reseated on the model and the impression materialallowed to set for about 5 minutes. Upon removal of the tray from themodel the impression material remained firmly adhered to the tray.

EXAMPLE 10

Using the method of EXAMPLE 9, an unirradiated customizable tray wasprepared and placed in a resealable polyethylene bag of dimensionsslightly greater than the tray. The bag was immersed in 70° C. wateruntil the full arch portion of the tray was transparent. The bag wasremoved from the water, and the bag and tray shaped to fit the full archof a "TYPODONT" model. After cooling, the custom tray was easily removedfrom the bag. The bag serves as a convenient custom tray enclosure thatdiscourages mess and contamination, and serves as a spacer between thedental tissue and tray. The spacer allows clearance for adequate amountsof impression material when a final impression is formed.

EXAMPLE 11

A dental die stone substitute was prepared by blending the ingredientsset out below in TABLE IX:

                  TABLE IX                                                        ______________________________________                                        Ingredient               Parts                                                ______________________________________                                        "TONE P-300" Polycaprolactone                                                                          39.3                                                 "CMD 8805" Urethane diacrylate                                                                         9.8                                                  CPQ                      0.5                                                  EDMAB                    0.5                                                  "EBERCRYL 830" Polyester hexacrylate                                                                   0.8                                                  "VICRON" Calcium carbonate                                                                             49.1                                                 ______________________________________                                    

at 80° C. until homogeneous. The resulting low viscocity thermoplasticmolding composition was tranferred to a syringe and delivered while warminto an inverted silicone elastomer full arch impression of a "TYPODONT"model. The impression was filled to above the gumline. The compositionwas irradiated on its back (gum) side only for 2 minutes with a"STAR-CURE" curing unit and transferred to a cold water bath for 2additional minutes. The solildified model was removed from the siliconeelastomer, yielding a rigid, highly detailed reproduction of thedentition. The solidified model was irradiated for an additional 2minutes, yeilding a model with excellent hot custom memory.

Although this invention has been described using certain illustrativeexamples, it should be understood that the invention is not limited tothe specific exemplary embodiments shown in this specification.

We claim:
 1. A method for making an impression of dental tissue,comprising the steps of:a) heating a molding composition to a molten orsoftened state, said composition comprising a thermoplastic,free-radically polymerizable material, and a free-radical initiator, thecomposition being solid at 38° C. and having a melting or softeningpoint that comfortably can be withstood by oral tissues, b) envelopingthe tissue with said molten or softened molding composition and ineither order, c) cooling the composition so that it solidifies; and d)causing or permitting the composition to undergo polymerization,wherebya semi-thermoplastic dental tissue impression having hot custom memoryis obtained.
 2. A method according to claim 1, wherein the compositioncomprises a polyester or a polyurethane.
 3. A method according to claim2, wherein the polyester comprises a segmented polyester.
 4. A methodaccording to claim 1, wherein the composition comprises apolycaprolactone.
 5. A method according to claim 1, wherein thecomposition comprises an acrylate or methacrylate.
 6. A method accordingto claim 5, wherein the acrylate or methacrylate comprises an acrylatedurethane oligomer or polymer.
 7. A method according to claim 1, whereinthe molten or softened molding composition is in the form of a warmarch-shaped tray.
 8. A method according to claim 7, wherein after hotcustom memory is imparted to the impression, an elastomeric dentalimpression material is placed in the impression and the impression andelastomeric material are placed in contact with dental tissue.
 9. Amethod for making a female model of a tooth or teeth, comprising thesteps of:a) heating a molding composition to a molten or softened state,said composition comprising a thermoplastic, free-radicallypolymerizable material, and a free-radical initiator, the compositionbeing solid at 38° C. and having a melting or softening point thatcomfortably can be withstood by oral tissues, b) shaping said molten orsoftened molding composition and in either order, c) cooling thecomposition so that it solidifies; and d) causing or permitting thecomposition to undergo polymerization,whereby a semi-thermoplastic modelhaving hot custom memory is obtained.